In the manufacture of resilient, resinous floor coverings it has long been desired to use polyurethane protective coatings as the top surface thereof, due to the very desirable properties and characteristics of polyurethane coatings which include good resistance to abrasion and solvent and chemical attack, good flexibility and impact resistance, good toughness, good high gloss retention, good surface texture, good adhesion to many materials, good weatherability, etc.
Unfortunately, although urethane coatings can normally be applied quite easily by dipping, spraying, brushing, rolling, and other conventional coating methods to adhere satisfactorily to a wide variety of materials, difficulties have been encountered in their application to foamable, resinous sheet materials wherein it is desired that the application of the urethane coating composition be conducted in an in-line manufacturing process wherein the urethane coating composition is applied in one step and the heating, blowing and foaming of the resinous sheet materials take place in another step in one passage through the manufacturing operation. To require two passages of the sheet materials through the manufacturing operation would, of course, be economically undesirable.
For example, if the urethane coating composition were to be applied in an in-line manufacturing operation by a conventional curtain coating procedure wherein the urethane coating composition is delivered in the form of a falling sheet or curtain to the foamable, resinous sheet material, difficulties are encountered because the variable speed required in the subsequent heating, blowing and curing operation was more or less incompatible with the preferably controlled, constant speed generally required of the curtain coating procedure. And, on the other hand, if a reverse-roll coating procedure were to be used which has a greater adaptability to the varying speeds of operation, difficulties were encountered in the obtaining of satisfactory, uniformly coated, bubble-free urethane top coatings.
Prior to the present invention, therefore, no completely commercially satisfactory or really successful manufacturing operation has been devised to provide for an in-line polyurethane coating operation and a resin blowing and curing operation in the resilient, resinous floor covering industry.